Metamorphic and sedimentary rocks thrust deep underground through seduction may eventually melt to form magma and cool into igneous rock once again. The entire process is called the rock cycle. The rock cycle takes many millions of years to complete, but it is the key to geologic change on our planet. The magma from the mantle comes out carrying the minerals and settles in cracks. Eventually, it cools down and solidifies to form igneous or metamorphic rocks.